The invention relates to a wireless network with at least one base station and a plurality of associated terminals for the exchange of useful data and control data.
The document xe2x80x9cETSI SMG2, Meeting No. 24, Cork Ireland, Dec. 1-5, 1997, Tdoc SMG2 359/97, Concept Group Alphaxe2x80x94Wideband Direct-Sequence CDMA (WCDMA), EVALUATION DOCUMENT (3.0), Part 1: System Description, Performance Evaluationxe2x80x9d proposes a radio network operating on the basis of CDMA (CDMA=Code Division Multiplex Access). The radio network consists of a plurality of radio cells with a respective base station and terminals or mobile stations present therein. After the registration and synchronization of a terminal, for example in the case of a request for a channel, a terminal transmits a random access burst via a random access channel (RACH). The random access burst consists of a preamble part and a data part. The preamble part consists of 16 symbols (preamble sequence) which is spread by an orthogonal Gold code (preamble code). The orthogonal Gold code contains 256 chip intervals. The data part contains a field with an identification for the terminal, a field for characterizing the requested service (short packet transmission, dedicated channel set-up etc.), an optional field for data packets (optional user packets) and a CRC field for error detection. A random access burst received by a base station is applied, via a matched filter, a preamble correlator and a peak detector, to a circuit section which estimates the time behavior of the data part and controls a RAKE circuit for evaluating the data part. Thus, in this case use is made of peak detection, based on correlation, and subsequent by message decoding. 80 random access channels are available to the terminals associated with a base station. These channels are determined by 16 different preamble codes and 5 different transmission instants. If two or more terminals transmit via the same random access channel, i.e. the same preamble code and the same transmission instant are chosen, a collision occurs and the information transmitted by the terminals cannot be correctly evaluated by the base station. Such collisions are likely notably in the case of high traffic loads.
It is an object of the invention to provide a wireless network in which a terminal exchanges signaling information with the associated base station in a different manner.
This object is achieved by means of a wireless network of the kind set forth which is characterized in that
the base station is arranged to transmit the starting instant of at least one signaling sequence of at least one terminal, and
that the base station includes a device for correlating a received signaling sequence and for detecting the pulse arising from a received and correlated signaling sequence.
In the context of the present application a wireless network according to the invention is to be understood to mean a network with a plurality of radio cells in which a respective base station and a plurality of terminals transmit control data and useful data in a wireless manner. A wireless transmission is intended to transmit information, for example via radio, ultrasound or infrared channels.
After registration and synchronization, a terminal must request a given useful channel from the associated base station in order to transmit useful data. Such a useful channel may be, for example a dedicated channel (for example, for the transmission of speech) either between the base station and the terminal or between two terminals. The channels are allocated by the base station. In accordance with the invention, a terminal transmits, via a signaling channel allocated by the base station, a request, for example for a dedicated channel. The base station should provide the terminal with at least the starting instant of a signaling sequence possibly known in advance. It is alternatively possible that, in addition to the starting instant, the terminals are also assigned one of a plurality of signaling sequences. A signaling sequence of this kind is a Gold or Kasami sequence having suitable autocorrelation and cross-correlation properties. The base station includes a device (for example, a matched filter) in which the received signaling sequences are correlated. The pulse resulting from the correlation is detected and assigned to a terminal. Because in the network according to the invention collisions are avoided because of the different starting instants of the signaling sequences and because no message decoding is performed after peak detection based on a correlation, but instead the occurrence of the pulse resulting from the signaling sequence is considered to be a signaling request, in comparison with the state of the art signaling detection can be performed in a more robust and faster manner, notably in the case of high traffic loads.
In order to detect a signaling sequence, a given time interval is selected for peak detection in dependence on the starting instant of the signaling sequence and on the channel properties. Such a time interval is referred to as a detection window. The length or duration and the starting instant of the detection window must be chosen in such a manner that peak detection is possible. The detection windows are smaller than the duration of the random access bursts known from the state of the art. Using the signaling according to the invention, therefore, many terminals can transmit a signaling request within a brief period of time.
In order to transmit a signaling sequence, after the registration and synchronization, a terminal in a radio cell always has the same starting instant in relation to a reference frame for as long as the base station does not explicitly change the starting instant. A signaling channel is thus permanently claimed for a terminal. Because many of such starting instants may be present in the reference frame of short duration (for example, 10 ms) and because all terminals of a radio cell use the same signaling sequence, the permanent assignment of a starting instant and a signaling sequence to a terminal requires only few network resources.
The signaling sequences of all terminals in a radio cell have different starting instants. In the simplest case the same signaling sequences are used by each terminal. The signaling sequences, therefore, may partly overlap, because the length of a sequence is usually greater than the spacing of two successive starting instants.
Another advantage of the network according to the invention consists in the reliability of the recognition of a signaling request. A detectable pulse is generated practically always after transmission of a signaling sequence. This is because interference signals and channel noise may cause xe2x80x9cartificialxe2x80x9d pulses at the output of the matched filter. It is very unlikely that they reduce the amplitude of the pulses at the output of the matched filter upon reception of an actually transmitted signaling sequence. In the worst case (for example, in the case of faults), a fault alarm is thus triggered if the amplitude of the noise or interference signal exceeds the detection threshold without a signaling sequence having been transmitted.
Patent claim 2 describes the characteristics for the correlation of the signaling sequences by means of a matched filter and the detection of the pulse by means of a peak detector. claim 3 describes the instant of transmission of the signaling sequence or signaling sequences to be used for the signaling, and the starting instants thereof, via a control channel. It is to be noted that the signaling sequence or sequences to be used for signaling are associated with only one base station only and not with its neighboring base stations. A Kasami or Gold sequence can be used as the signaling sequence (claim 4). However, the use of other orthogonal square-wave signals is not precluded.
The starting instants of the same signaling sequences may either be situated at the same constant distance from one another or at an individually determined distance (claims 5 and 6). In the former case the constant distance is dependent, for example on the worst channel properties, whereas in the second case it is dependent on the respective channel properties between the base station and the relevant terminal.
The claims 7 and 8 describe the characteristics for the transmission of 1-bit signaling information and n-bit signaling information, respectively (n greater than 1 and integer). Furthermore, different signaling sequences can be transmitted in a radio cell when the traffic load is very high and no further starting instants of a signaling sequence can be allocated (claim 9).
The claims 10 to 12 relate to embodiments of a base station and a terminal.
The wireless network according to the invention is further advantageous in that the amplitude of the signaling sequence can always be adapted to certain network requirements. If the amplitude of the signaling sequence is too low, it is increased (claim 13). This may also be effectedxe2x80x94as described in patent claim 2xe2x80x94by a step-by-step adaptation process. This process ends if an acknowledgement is given by the assigned base station within a predefined period of time or if the signaling sequence has maximum amplitude. Such an acknowledgement is, for example, the assignment of a user channel to the terminal (claim 15).
The invention also relates to a method of exchanging useful data and control data between at least one base station and a plurality of associated terminals in a wireless network, to a base station in a wireless network for the exchange of useful data and control data with a plurality of associated terminals, and to a terminal in a wireless network for the exchange of useful data and control data with at least one base station.